Mixing devices are in wide use in industry, and many mixing devices include a large vessel which contains a liquid or other material to be mixed. In some types, a typically vertically-oriented impeller shaft runs down some or all of the length inside the vessel. The impeller shaft typically enters the vessel through a bearing and seal arrangement, and the impeller shaft is rotatably driven from outside of the vessel usually by a motor located at the top of the vessel. Inside the vessel, at one or several axial locations on the length of the shaft, radially extending impellers are attached to the shaft which have paddles or blade type features extending radially outwardly. Rotation of the shaft rotates the impellers to mix and or otherwise impart energy to the fluid or other material inside the vessel.
In some instances, the motor and drive assembly, along with the bearing and sealing arrangement, are mounted at the top opening of the vessel, and the shaft is suspended, so that it hangs down from the motor with its lower end being either a free end spaced above the bottom of the vessel, or a lower stub of the shaft may be rotatably supported by a bearing at the bottom inside of the vessel. In the case of long shafts, intermediate steady bearings may be mounted to provide radial support against flexing or bending or vibration of the shaft.
In some instances, the impellers themselves are welded directly onto the shaft at the time of manufacture. This arrangement is often suitable, but also can have the disadvantage that welding of the impellers onto the shaft is relatively permanent. Thus, replacement or substitution of different impellers for different applications is not convenient. Further, the opening in the top of the vessel needs to be large enough to permit a shaft, and the welded impellers all to be inserted through the opening when installing the shaft in the impellers into the vessel. This can require a large opening in the top of the vessel.
To overcome these disadvantages, there are arrangements in which a removable or detachable hub that supports the impellers can be mounted onto the shaft. However, at least some of the removable hub designs suffer from the disadvantages that all of the impellers are mounted to a single removable hub, and thus the hub and impeller assembly, which may be quite large, still needs to fit through the opening in the vessel. Further, some of these arrangements have a disadvantage that they may not be as sanitary as the desired. In many applications, it is desirable to have a very sanitary arrangement which reduces as much as possible any of the mixing material from going into the inside structure of the hub mounting arrangement. Entry of the material into the inside structure of the hub mounting arrangement, and into any gaps, crevices or clearances between the hub and the shaft, can be undesirable because it can lead to difficulty in cleaning the installed arrangement and possible contamination of the material being mixed.
In view of the foregoing, there is a need in the art for a removably attachable impeller hub that can quickly and easily be attached and/or detached to an impeller shaft, which can provide a secure attachment while also having desirable sanitary properties.